Injection of premixed concentrated chemical solution in steam generator chemical cleaning

ABSTRACT

A steam generator chemical cleaning system is provided wherein a concentrated chemical cleaning solution is premixed off-site in sufficient volume and concentration to allow the dilution to proper cleaning level be achieved by slow injection into the generator when filled with demineralized water. The premixed chemicals are transported in a tanker to the generator site and injected therein directly from the tanker.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to cleaning of steam generators and more particularly to chemical cleaning using a range of chemical concentrations from dilute to concentrated.

2. Description of the Prior Art

In prior art chemical cleaning of steam generators, each bulk chemical used for the cleaning, approximately six different chemicals, was transported on-site in individual tankers, tote containers, or drums and then added to a stationary tank large enough to supply the required volume of solvent for a cleaning removal step. Once the chemical solvent was prepared at the final desired concentrations and heated to the optimum temperature for each chemical cleaning step, the chemical solvent was pumped directly to the steam generators to remove corrosion deposits.

In such prior art chemical cleanings, a group of employees arrived on-site before the cleaning to receive the chemicals, constructed the berms for the chemical tankers and mixing tanks, and then mixed the chemicals with demineralized water in tanks to manufacture the desired concentration of chemicals for the solvents. Once the berms were constructed and the chemical solvents were prepared, the set-up of the chemical cleaning system was considered complete. The chemical solvent for each chemical cleaning step was heated, if appropriate for the application, and pumped directly to the steam generator(s) being cleaned. Once the application was complete, the chemical cleaning solvent was drained from the steam generator(s) and sent to waste processing for proper disposal. When all of the cleaning application steps were complete, a group of workers would then have to dismantle the large berms associated with each chemical tanker and mixing tanks. This application method required a significant amount of on-site time, financial investment of the utility, due to the additional time to set-up and tear down the large chemical cleaning system and the on-site mixing of the chemicals and demineralized water for each chemical cleaning step, as well as requiring a large area of site property to accommodate the chemical cleaning system footprint.

The problem with the prior art cleaning methods was always the amount of on-site time and space required. Much on-site time was needed to construct and dismantle the berms required for each chemical tanker and mixing tank, and to mix the chemicals and demineralized water. Additionally, time on-site required more cost to the utility. The above system also requires a large amount of space to store the chemical tankers and mixing tanks. Sites usually have limited available land near containment, and the further away the tankers and tanks are, the greater the total system volume needed to fill the process lines to the steam generators. Longer process lines also tend to increase the chances for heat and pressure losses. Cost to the utility does increase when a greater total system volume is needed due to long process lines.

In other prior art cleaning application methods, the concentrated chemicals were known to be mixed in the steam generator. When performing this technique, there was no recirculation loop and the concentrated chemicals were injected into the steam generator through the blowdown line. Depending on where the corrosion deposits were located in the steam generator, venting was induced at different levels of filling to mix the solution. This technique did mix the concentrated chemicals; however, it did not mix the solution instantaneously.

Another limitation with the prior art systems of mixing the concentrated chemicals in the steam generator(s) is that the severity and location of the corrosion deposits have to be known. Knowing the composition and location of the deposits is important because the concentration of each chemical being injected has to be correct in order to effectively remove the deposits and mitigate further corrosion. If the information regarding the deposits was inaccurate, then the wrong concentration of chemicals could be injected into the steam generator(s) and could induce further corrosion and result in further damage the steam generator(s).

Thus a simple system of providing custom measured chemicals directly to the generator and then recirculating them therein for a complete cleaning which required little on site property space and setup time was in high demand.

SUMMARY OF THE INVENTION

The present invention solves the above mentioned steam generator cleaning problems and others by having the chemicals premixed in concentrated form at an off-site facility, and then bringing them on-site in road tankers. The premixed concentrated chemical solution will contain the correct volume of each bulk chemical needed for the specific removal step to achieve the desired concentration of the individual constituents upon dilution to full volume within the steam generator(s) being chemically cleaned. When the chemical injection step is ready to be performed, the tanker containing the premixed chemicals will simply be connected to the chemical injection system through a prestaged manifold connected to the steam generator recirculation system. The chemical cleaning system will be connected to the steam generator(s) in two locations, preferably one in the lower region of the generator and the other in the upper region of the generator, in order to achieve a recirculation loop through the steam generators for the chemical cleaning system.

In using this system of the present invention, the steam generator(s) is partially filled with demineralized water, essentially the volume required to dilute the concentrated chemicals to the desired concentration while concurrently achieving the final fill volume of the steam generators, typically just above the top of the tube bundle. Next, the steam generator system volume will be placed on recirculation where suction is taken on the lower region of the generator and the liquid returned in the upper region of the generator to complete the loop through the connected chemical cleaning system. A chemical injection pump is then used to add the chemicals to the demineralized water in the system's recirculation loop while the system is already in recirculation and at the proper temperature. The recirculation loop contains the demineralized water that dilutes the chemicals as it is mixed. The concentrated chemicals will be mixed such that the concentration of the chemicals as they reach the steam generator(s) will not exceed the approved maximum concentration for the system. Bleeding the chemicals gradually and taking samples for chemical analysis ensures that the system will achieve, and not exceed, the approved chemical concentration. Exceeding the approved chemical concentration could induce corrosion and other factors that could damage the steam generators.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is basic process diagram of the chemical cleaning system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawing it will be seen that a concentrated chemical cleaning system (10) is shown wherein a concentrated cleaning chemical solution which has been premixed at an off-site facility was loaded on a tanker (12) and brought to the site of a steam generator (14) which will be cleaned. A chemical injection pump (16) is connected to the tanker (12) and injects the premixed concentrated chemical solution contained therein into a recirculation loop through the steam generator (14) as will be described later.

To start the cleaning the steam generator (14) is filled with demineralized water to a volume sufficient to dilute the concentrated chemicals in the tanker (12) to the desired concentration when fully injected into the steam generator (14). This usually involves filling it above the top of the tube bundle (not shown). Once this is done the water is recirculated through the steam generator by a recirculation pump (18) which draws the water along line (20) to the recirculation pump (18) from a lower level opening (22) in the steam generator (14). The water is then exhausted along line (24) to line (26) which is connected to the inlets of a cooler (28) a heater (30) and an ion exchanger column (32). These inlets are controlled by respective control valves (34, 36, 38) which are selectively opened and closed by a control system (not shown) which senses the temperature and condition of the water in the generator (14) and controls the valves (34, 36, 38) to achieve the proper water temperature and conditioning. The exhausts of the cooler (28) the heater (30) and the ion exchange column (32) are controlled by respective valves (40, 42, 44) which are controlled by the control system (not shown) to feed the water to a line (46) and there through to an upper level inlet (48) of the generator (14).

This recirculation continues until the proper water conditions are met at which time the chemical injection pump (16) is activated by the control system (not shown) to start adding the concentrated chemical solution from the tanker (12) to line (26). This addition is done in small doses into the water recirculation loop until the desired concentration for proper chemical cleaning is achieved. While the recirculation pump is on, a sample of the water concentration in the generator (14) is taken along line (50) to a monitor (52) which measures the volume and sends this signal to the control system (not shown) along line (54). When off normal conditions are sensed, the control system shuts off the injection pump and continues the recirculation until the conditions are rectified. After the steam generator (14) is cleaned, the recirculation pump (18) is shut off, a valve (56) is opened and the water is allowed to drain from the generator (14) along line (58) to a waste tanker (60) for disposal.

It will now be obvious that the invention of having the chemicals mixed together into the desired concentrated chemical solutions off-site saves time on-site and usage of site property. It takes additional on-site time and costs to construct berms for the large chemical and mixing takes, and to make concentrated chemical solvents for each chemical cleaning step. Having the concentrated chemical solutions premixed off-site is much more cost and time efficient. In utilizing site property, transporting in premixed concentrated chemical solutions requires no further mixing of chemicals on-site external to the steam generator system. Less site property is used because the need for chemical tankers, mixing tanks, and berms needed for those tankers and tanks is alleviated since no mixing of chemicals is required on-site. Chemical tanks and tankers typically require the largest area footprint in chemical cleanings. Additionally, the chemical tankers injecting the pre-mixed chemicals utilizing the recirculation loop created with the chemical cleaning hoses and other equipment, allow the concentrated chemicals to be added to the system gradually. The recirculation of the solvent provides the necessary mixing to ensure that the qualified concentrations are not exceeded and adequate solvent is supplied for optimum deposit removal.

When the chemical cleaning is completed the generator (14) is flushed with clean demineralized water. To conserve water the bottom outlet (22) of the generator is connected to pump (18) to pump the water along line (20) to the line (26) and along now open valve (38) to the ion exchanger column (32) for demineralization. The cleaned water is exhausted along line (68) to open valves (44) and (42) to line (46) and back to the top inlet (48) of the generator (14). Thus the water may be recirculated through the ion exchanger column (32) to completely flush and remove minor solvent concentrations from generator (14).

It will be understood that certain obvious details have been deleted herein for the sake of conciseness and readability but they are intended to fall within the scope of the following claims. 

1. A method of chemically cleaning a steam generator comprising the steps of: premixing a concentrated solution of chemicals for a steam generator off-site from the generator; delivering the premixed solution to the site of the generator; partially filling the generator with demineralized water; recirculating the water in the generator through equipment for bringing the water to proper chemical cleaning conditions; injecting the premixed solution into the recirculated water until the solution is diluted to proper generator cleaning concentrations and levels; and cleaning the generator with the diluted premixed chemical solution.
 2. A method as set forth in claim 1 including the step of drawing the chemical solution from the generator to a waste tanker for off-site disposal.
 3. A method as set forth in claim 1 including the step of stopping the injection of premixed solution after it reaches generator cleaning levels and maintaining the recirculation thereof.
 4. A method as set forth in claim 1 including the step of sensing the chemical concentration in the generator during the step of injecting the premixed solution into the recirculated water.
 5. A method as set forth in claim 1 including the step of loading a volume of premixed concentrated chemical solution into a tanker volume to dilute the demineralized water in a water filled generator to proper cleaning levels when fully injected into the generator.
 6. A method as set forth in claim 1 including the step of flushing the generator with clean demineralized water after the completion of the chemical cleaning process.
 7. A method as set forth in claim 6 wherein the flushing water is recirculated through an ion exchanger column to completely clean the generator. 